Grids in backside illumination image sensor chips and methods for forming the same

Abstract

A device includes a semiconductor substrate having a front side and a backside, a photo-sensitive device disposed on the front side of the semiconductor substrate, and a first and a second grid line parallel to each other. The first and the second grid lines are on the backside of, and overlying, the semiconductor substrate. The device further includes an adhesion layer, a metal oxide layer over the adhesion layer, and a high-refractive index layer over the metal layer. The adhesion layer, the metal oxide layer, and the high-refractive index layer are substantially conformal, and extend on top surfaces and sidewalls of the first and the second grid lines.

What is claimed is: 
     
       1. A method comprising:
 forming a grid layer on a backside of a semiconductor substrate; 
 patterning the grid layer to form a grid comprising a plurality of grid lines, wherein each of grid openings of the grid between the plurality of grid lines is aligned to one of a plurality of image sensors in the semiconductor substrate; 
 depositing an adhesion layer on sidewalls and top surfaces of the a plurality of grid lines; 
 forming a metal oxide layer over the adhesion layer; 
 depositing a dielectric layer over the metal oxide layer; and 
 removing portions of the adhesion layer, the metal oxide layer, and the dielectric layer from the grid openings. 
 
     
     
       2. The method of  claim 1 , wherein the depositing the adhesion layer and the forming the metal oxide layer comprise:
 depositing the adhesion layer; and 
 oxidizing a top portion of the adhesion layer, with a bottom portion of the adhesion layer remaining. 
 
     
     
       3. The method of  claim 2 , wherein the oxidizing the top portion of the adhesion layer comprises treating the deposited adhesion layer in an oxygen-containing gas. 
     
     
       4. The method of  claim 1 , wherein the forming the grid layer comprises depositing a metal layer. 
     
     
       5. The method of  claim 1 , wherein after the removing, the adhesion layer, the metal oxide layer, and the dielectric layer comprise remaining portions on sidewalls of the grid lines. 
     
     
       6. The method of  claim 1 , wherein after the removing, the adhesion layer, the metal oxide layer, and the dielectric layer comprises remaining portions overlapping the grid lines. 
     
     
       7. The method of  claim 1  further comprising:
 forming color filters and micro-lenses overlapping the plurality of image sensors. 
 
     
     
       8. The method of  claim 7  further comprising:
 filling an oxide layer into the grid openings; and 
 planarizing the oxide layer, with the color filters and the micro-lenses overlapping portions of the oxide layer in the grid openings. 
 
     
     
       9. A method comprising:
 forming a plurality of image sensors on a front side of a semiconductor substrate; 
 forming a grid layer on a backside of the semiconductor substrate; 
 patterning the grid layer to form a plurality of grid lines, wherein grid openings between the plurality of grid lines are aligned to the plurality of image sensors; 
 forming a stacked layer on top surfaces and sidewalls of the plurality of grid lines, wherein the forming the stacked layer comprises:
 forming an adhesion layer; 
 forming a metal oxide layer over the adhesion layer; and 
 forming a dielectric layer over the metal oxide layer; and 
 
 patterning the stacked layer to remove portions of the stacked layer aligned to the plurality of image sensors. 
 
     
     
       10. The method of  claim 9 , wherein after the stacked layer is patterned, each of the adhesion layer, the metal oxide layer, and the dielectric layer comprises portions on sidewalls of each of the plurality of grid lines. 
     
     
       11. The method of  claim 9 , wherein after the patterning, each of the adhesion layer, the metal oxide layer, and the dielectric layer comprises a portion overlapping each of the plurality of grid lines. 
     
     
       12. The method of  claim 9  further comprising forming an additional image sensor on the front side of the semiconductor substrate, wherein after the patterning the grid layer, a portion of the grid layer is left over and aligned to the additional image sensor, and wherein after the stacked layer is patterned, a portion of the stacked layer is left over and aligned to the additional image sensor. 
     
     
       13. The method of  claim 9 , wherein the forming the adhesion layer comprises depositing a chromium layer. 
     
     
       14. The method of  claim 9 , wherein the forming the metal oxide layer comprises forming a chromium oxide layer. 
     
     
       15. The method of  claim 9 , wherein the forming the adhesion layer and the forming the metal oxide layer comprise:
 depositing the adhesion layer comprising a metal; and 
 oxidizing a surface layer of the adhesion layer to form the metal oxide layer, wherein a inner layer of the adhesion layer is not oxidized. 
 
     
     
       16. The method of  claim 9 , wherein the forming the grid layer comprises:
 forming a titanium nitride layer; and 
 forming a tungsten layer over the titanium nitride layer. 
 
     
     
       17. A method comprising:
 forming a plurality of image sensors on a front side of a semiconductor substrate; 
 forming a buffer oxide layer on a backside of the semiconductor substrate; 
 forming a first metal layer on the backside of the semiconductor substrate, wherein the first metal layer is over the buffer oxide layer; 
 etching the first metal layer to form a metal grid comprising grid lines and grid openings between the grid lines; 
 forming a metal oxide layer comprising sidewall portions on sidewalls of the grid lines; and 
 forming a dielectric layer comprising sidewall portions on the sidewall portions of the metal oxide layer; 
 filling a transparent material into the grid openings; and 
 forming color filters overlapping portions of the transparent material in the grid openings. 
 
     
     
       18. The method of  claim 17 , wherein the forming the metal oxide layer and the forming the dielectric layer comprise:
 forming a conformal blanket metal oxide layer; 
 forming a conformal blanket dielectric layer over the conformal blanket metal oxide layer; and 
 removing portions of the conformal blanket metal oxide layer and the conformal blanket dielectric layer from the grid openings. 
 
     
     
       19. The method of  claim 17 , wherein the forming the metal oxide layer comprises:
 forming a second metal layer as a blanket layer covering the metal grid; and 
 oxidizing a top portion of the second metal layer. 
 
     
     
       20. The method of  claim 17 , wherein the metal oxide layer comprises chromium oxide.